Various mixing devices for fluid materials are known. One general type of mixing device comprises a generally tubular column along which the two or more fluid materials are caused to flow together, the tubular column having internal turbulence-creating elements which engage with and cause turbulence in the flow of fluid materials along the column. The turbulence causes the materials to mix thoroughly. One such mixing device is disclosed in U.S. Pat. No. 4,767,026, which comprises a tubular column within which are a number of baffles in the form of helically twisted ribbons, the ribbons alternating in their direction of helical twist along the length of the column. The mixing device of U.S. Pat. No. 4,767,026 is disclosed in combination with a dispensing device for two fluid materials. Another such mixing device is disclosed in EP 0212290 A which comprises a cylindrical passage tube provided with a groove on its inner peripheral wall and a shaft with a helical groove on its outer peripheral surface. The grooves on the shaft and the passage tube are of unchanging depth along the length of the tube.
Known mixing devices are inadequate for the thorough mixing of certain materials, e.g. medicinal or other healthcare formulations which comprise two or more fluid materials each of which contain substances which are intended to interact on mixing to form a product.
It is an object of this invention to overcome this problem, in part at least, and also to provide an alternative to known mixing devices. It is also an object of the present invention to provide a mixing device which is suitable for use with the type of small volume hand operated dispensing devices often used for healthcare products, such as toothpastes, gels etc. These generally comprise a number of reservoirs for the respective substances each reservoir communicating with a hand operated pump which pumps the substance through a respective communicating dispensing outlet. Such dispensing devices are well known, for example in U.S. Pat. Nos. 5,104,004 and 4,438,871 among many others. Other objects and advantages of the present invention will be apparent from the following description.